1. Field of the Invention
The present invention relates to an image capturing unit, a color measuring device, a color measuring system, an image forming device, and a color measuring method, and specifically, to an image capturing unit, a color measuring device, a color measuring system, and an image forming device for stably imaging a subject and a reference chart.
2. Description of the Related Art
An image forming device such as a color ink injection image forming device, a color electrophotography image forming device, and the like is used in offset printing of advertising media, pamphlets, and the like of which the number of print copies are relatively small but high image is demanded with improvement in image quality.
In the offset printing in which high image quality is demanded, the color of the printed material demanded by a customer and the color of the print output result that is actually printed and output with the image forming device sometimes differ.
The customer normally checks the color of the printed material on a display and then orders the print, but the image forming device has a color reproducing property unique to each model and may provide a printing result different from the color checked on the display.
A technique of performing color reproduction using a color space, for example, L*a*b* color space and xyz color space that does not depend on the device such as the display and the image forming device is thus used from the prior art.
The image forming device controls the amount of color material, and the like to output a specified color. For example, in the ink injection image forming device, the discharging amount of ink, the print pattern, and the like are calculation controlled, where the discharging amount of ink from the ink head is controlled to control the output color. In the electrophotography image forming device, the attaching amount of toner to a photosensitive element, the light quantity of the laser beam, and the like are controlled to control the output color.
However, the amount of color material, for example, the discharging amount of ink in the ink injection image forming device fluctuates according to the state of the nozzle of the head, viscosity fluctuation of the ink, the fluctuation of the discharge drive element (piezo element, etc.), and hence causes fluctuation in color reproducibility. Furthermore, the discharging amount of ink in the ink injection image forming device may change over time in one image forming device or may differ for each image forming device, and hence the color reproduction of the image may fluctuate for every image forming device.
In the image forming device, therefore, color adjustment processing is conventionally carried out to suppress the fluctuation of output due to the properties unique to the device and enhance the reproducibility of the output with respect to the input. In the color adjustment processing, for example, an image (reference color patch image) of a color patch of a reference color is actually output by the image forming device, and the reference color patch image is performed with color measurement by the color measuring device. A color conversion parameter is generated based on a difference between a color measurement value of the reference color patch image, which is performed with color measurement by the color measuring device, and a color value in a standard color space of the corresponding reference color, and such color conversion parameter is set to the image forming device. Thereafter, when outputting an image corresponding to the input image data, the image forming device performs color conversion on the input image data based on the set color conversion parameter, and records and outputs the image based on the image data of after the color conversion is performed to suppress the fluctuation in the output caused by the properties unique to the device and achieve the image output of high color reproducibility.
In the conventional color adjustment processing, spectrophotometric color measuring device is widely used as a color measuring device for performing color measurement on the reference color patch image, which spectrophotometric color measuring device can obtain spectral reflectivity for every wavelength and thus can carry out highly accurate color measurement. However, the spectrophotometric color measuring device is an expensive device mounted with a great number of sensors, and thus highly accurate color measurement is desired to be carried out using a less expensive device.
Conventionally, there is provided a color measuring device including a reference color measuring means for performing color measurement on a reference color chart in advance to obtain a hue reference value with RGB data, a color image input unit for obtaining the RGB data by imaging a subject including the reference color chart and a body to be performed with color measurement simultaneously or separately, an image extracting means for extracting the RGB data of the reference color chart and the RGB data of the body to be performed with color measurement from the RGB data obtained by the color image input unit, and a calculating means for obtaining a difference between the RGB data of the reference color chart obtained by the image extracting means and the RGB data of the reference color chart obtained with the reference color measuring means, and correcting at least the RGB data of the body to be performed with color measurement using the difference (see Japanese Unexamined Patent Publication No. 5-223642). In the prior art, the reference color chart, which serves as a comparison target of the subject, is placed near the subject to be performed with color measurement, the subject and the reference color chart are simultaneously imaged with a color video camera serving as the color image input unit, the RGB data of the subject is corrected using the RGB data of the reference color chart obtained by the imaging, and then the RGB data of the subject is converted to a color value in the standard color space.
However, in the prior art described in the above publication, the positional relationship between the reference color chart, which is imaged as a comparison target of the subject, and the color image input unit is difficult to maintain constant for each imaging, the image capturing conditions change for every imaging and stable imaging is difficult to carry out.
Therefore, there is a need for an image capturing unit, color measuring device, image forming apparatus, a color measuring system, and a color measuring method that are capable of capturing the subject and the reference chart in a stable positional relationship.